1. Field of the Invention
The present invention relates to an image forming device such as a copier, a printer and a facsimile machine.
2. Description of the Related Art
A known electrophotographic image forming device uses a photoconductive drum as an image carrier. The image forming device forms an electrostatic latent image on a surface of the image carrier, and adheres toner onto the electrostatic latent image to form a visible image. Then, the image forming device transfers the toner image onto paper. In such an image forming device, in general, paper is transported from a paper feed unit to a printer unit, and the printer unit performs an image forming process on the paper. Then, the paper is output onto an output tray. Depending on the environment, the paper may curl while being transported. Thus, there exists a demand for an image forming device which can accurately transport the paper even when the paper curls. In particular, since the paper is heat-processed by a fixing roller after the toner image is transferred onto the paper during the image forming process, when the paper curls it causes an output movement of the paper onto the output tray to be unstable.
A conventional image forming device includes a pair of upper and lower output rollers, a plurality of firmness-providing rollers, and a moving member. The output rollers sandwich the paper after an image has been fixed on the paper, and output the paper. The firmness-providing rollers are movable in an axial direction of the output rollers. The moving member moves the firmness-providing rollers to a position where the firmness-providing rollers provide firmness to the paper according to a kind of the paper to be output. Additionally, a pressing force regulating plate regulates a pressing force between a drive roller and a pressure roller to correct a curl of the paper. By alternately providing film members protruding into a paper transportation path, the firmness of thin paper may be reinforced.
As described above, when the paper curls, an output movement of the paper onto the output tray becomes unstable. Moreover, when curled papers are output onto the output tray, the output papers cannot be stacked neatly. As a result, handling of the papers becomes extremely inconvenient. Such a curl of the paper differs according to a material and/or a size of the paper or even according to an environment. Thus, the curl of the paper is diverse and difficult to uniformly deal with. As described above, conventional image forming devices have dealt with the curl of the paper by adding firmness to the paper. However, this is not sufficient for dealing with various curls of the paper.